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1.. SPDX-License-Identifier: GPL-2.02 3High Level Design4=================5 6An ext4 file system is split into a series of block groups. To reduce7performance difficulties due to fragmentation, the block allocator tries8very hard to keep each file's blocks within the same group, thereby9reducing seek times. The size of a block group is specified in10``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 *11``block_size_in_bytes``. With the default block size of 4KiB, each group12will contain 32,768 blocks, for a length of 128MiB. The number of block13groups is the size of the device divided by the size of a block group.14 15All fields in ext4 are written to disk in little-endian order. HOWEVER,16all fields in jbd2 (the journal) are written to disk in big-endian17order.18 19.. include:: blocks.rst20.. include:: blockgroup.rst21.. include:: special_inodes.rst22.. include:: allocators.rst23.. include:: checksums.rst24.. include:: bigalloc.rst25.. include:: inlinedata.rst26.. include:: eainode.rst27.. include:: verity.rst28